Taurus and LORITA - A High Arctic Success Story

A large number of Nanometrics Taurus Digital Seismographs were recently deployed on the ice between Ellesmere Island, in the Canadian High Arctic, and Greenland.

The 150 unit Taurus deployment in April and early May 2006 was part of a wide angle reflection/refraction survey of the Lomonosov Ridge, a submarine mountain range of the Lincoln Sea. The joint Canada-Denmark expedition "Lomonosov Ridge Test of Appurtenance" or LORITA-1, was conducted to support offshore sovereignty claims by both Canada and Greenland (Denmark).

According to the project Chief Scientist, Dr. Ruth Jackson of Natural Resources Canada, "without the Taurus, LORITA would not have been successful due to the persistent poor weather. The Taurus's low-power consumption, continuous recording, large data storage capacity and reliability in extreme cold weather made the difference."
 

PROJECT BACKGROUND

Ellesmere Island (Canada) is adjacent to Greenland (Denmark) and both countries have the right to claim a 400 km long submarine mountain range named Lomonosov Ridge as a natural extension of their land mass under the United Nations Convention on the Law of the Sea (UNCLOS). A scientific expedition was established as a joint effort between the countries to gather a combination of bathymetry, seismic and gravity data in order to substantiate the claim of the ridge.

With project operations based out of the Canadian Forces Station Alert, the most northern permanently inhabited settlement in the world (82°30’06” N), a team of 30 scientists spent all of April and early May gathering seismic data while facing the challenges of the high Arctic winter. Over the expedition period, the team encountered varying field conditions with temperatures dipping below -30 C, drifting and broken sea ice, fog, blizzards and high winds
 

SEISMIC WORK

A wide angle reflection/refraction technique was employed with the use of explosives as an acoustic source. The team used this method to provide detailed information on the distribution and thickness of the subsurface layers down to a depth of 40 km. A figure on the side shows the shot and receiver lines. Due to weather challenges, 100 "receivers" per line was typical. Each receiver consisted of a Taurus DAS, Geophone and battery packaged in a thermally insulated container designed and prepared by Natural Resources Canada. Data Availability was in excess of 99.999% with more than 2300 recordings in the final data set.

After each successful blast, the expedition was able to retrieve the receivers from the field and quickly pull the data from the Taurus to check data quality and perform initial analysis. Using Nanometrics’ Apollo Project software, the team was able to retrieve shot data from all the units simultaneously over a local area network via a single web browser.
 

THE CHALLENGES AND TAURUS SOLUTION

The initial challenge for the expedition was in selecting a reliable digital seismograph system that was small enough when combined with seven days supply of batteries, to maximize helicopter efficiency (carry the most receiver kits per flight). With unknown ice conditions, unpredictable weather and complicated logistical procedures, the scientists required an easy-to-use seismograph capable of reliably recording large volumes of continuous data without the typical constraints and additional stress of managing shot windows.

This concern was realized as the weather closed in towards the end of one of the 100 instrument deployments. When the weather cleared 7 days later, there was concern that the instruments could not be picked up, batteries serviced and re-deployed before the weather deteriorated again. A check of 5 spare kits out on the ice near the base revealed that all were still working well. The decision was made to "fire the shot". Excellent data were retrieved from all units. An instrument with higher power consumption and/or one that required timed shot windows would have meant that all receivers had to have been picked up and serviced, costing time and, more important, a missed data collection opportunity.

Studies on drifting sea ice create additional challenges. Major sections of ice can fissure and break off from adjacent ice. The LORITA team experienced this first hand. During retrieval of one group of Taurus receivers, the line ended abruptly about halfway through the pick-up process. The team had planned for this contingency by placing GPS position beacons along the lines, spaced approximately every 5 receivers. Returning to base and consulting the map display they could see what had happened. Upon returning to the area they found the remaining section of the line displaced 16km from the first part of the line. The Taurus data were still useful since the Taurus data is self-describing, including latitude and longitude information in each data packet.
 

THE TAURUS PORTABLE DATA ACQUISITION SYSTEM

Following an extensive marketplace specification review and side-by-side product testing, the Taurus seismograph was chosen for the expedition for these key benefits:
 

  • Continuous Recording
  • Small Size, Light Weight and Portability
  • Very Low Power consumption (~700mW)
  • Reliability, especially in temperataures < -30 degreec C

 

Continuous Recording

The large data storage capacity of the Taurus (combined with the very low power consumption) enabled the units to be set-up with recording started prior to loading the units on the helicopter for deployment. This capability significantly reduced the time to deploy and changed the exercise from one of field set-up to simple drop, install the geophone and go.

Small and light weight equals portability

The major costs of most scientific expeditions is not the instrumentation, but the cost to deploy - especially if an instrument will be deployed and re-deployed over the course of the project. When working in environments with unpredictable and harsh weather and/or remote, inaccessible terrain, deployment logistics can make the difference between success and failure. The smaller and lighter the instrument package, the easier it is to transport and deploy. Reducing deployment time means less deployment cost. As the LORITA team members discovered, it can also make the difference between getting the necessary data or not when bad weather sets in.

Very Low Power Consumption

Low power consumption contributed to the project's success in several ways. For any given planned operational window, the lower the power consumption, the smaller and lighter the total package due to battery savings in size and weight. Whether instruments are deployed by helicopter, on foot or by road, the less equipment you need and the lighter the package, the easier it is to manage.

The LORITA scientists also benefited from the low power consumption through longer deployment cycles. The extended field time afforded by the low power consumption allowed scientists to reduce the number of recovery cycles and maximise the number of shots per deployment.

Reliability

The Taurus was tested at temperatures below -30 degrees C and was the only unit tested that could reliably meet the cold temperature operational requirements. This reliability was central to the project's success.

As the manufacturer, Nanometrics designed, built and tested the Taurus for demanding field environments like the High Arctic. While we have every confidence that our equipment will perform well, it is only through success stories such as the LORITA expedition that we have an opportunity to examine the real-world performance and truly confirm our expectations. The Taurus is an instrument that Nanometrics is confident will contribute to the success of other projects. Whether the objective is Volcano Monitoring, after-shock studies or passive seismic tomography or other projects, when deployment costs must be managed and high data availability is the objective, Taurus will deliver - but don't take our word for it, take LORITA's.
 

EXPEDITION LINKS

For more information regarding the expedition, please visit:
 

 

* All photos courtesy of the LORITA Project (Geological Survey of Denmark and Greenland (GEUS) and Natural Resources Canada- Geological Survey of Canada (NRCAN-GSC)) 

Sep 26, 2008

Tags: General News